1. Field of the Invention
The present invention relates to an Internet protocol television (IPTV) service system, and more particularly, to an IPTV service system for efficient multicast of a motion picture expert group-transport stream (MPEG-TS), and a method thereof.
The present invention has been derived from a research conducted as a part of information technology (IT) new growth power core technology development business by Ministry of Information and Communication, Republic of Korea (Project management No.: 2005-S-058-01, Project title: Development of Network/Service Control Technology in All-IP based Converged network).
2. Description of the Related Art
In general digital broadcasting, broadcasting data are transmitted according to MPEG-TS, which is a transmission standard format of the MPEG. The MPEG-TS is delivered to a set-top box connected to a customer premises terminal through a variety of broadcasting delivering networks such as a terrestrial TV network, a satellite TV network, and a cable TV network.
In the case of an IPTV service, broadcasting data are delivered through an IP network, which is different from the digital broadcasting in which broadcasting data are delivered through a terrestrial TV network, a satellite TV network, and a cable TV network.
However, since a current broadcasting station produces broadcasting data in a MPEG-TS format and transmits the same, the IPTV service merely carries the MPEG-TS from the broadcasting station over an IP network, with or without additional processing on the MPEG-TS.
FIG. 1 is a view illustrating the construction of a general MPEG-TS.
Referring to FIG. 1, the MPEG-TS includes a plurality of elementary streams (ES) which are audio, video, and data streams forming broadcasting data, respectively.
Also, the MPEG-TS includes a program association table (PAT) having packet identification (PID) values of a program map table (PMT), and the PMT which have a PID list of individual elementary streams such as a video stream and an audio stream.
Besides, program and system information (PSI) such as a master guide table (MGT), a virtual channel table (VCT), and a rating region table (RRT) for respectively defining a program guide, channel configuration information, and rating information can be inserted together to the MPEG-TS, and these tables are referred to as program and system information protocol (PSIP) data.
Each ES and table of PSIP data are identified with the PID, which is assigned for each stream and table. For example, the PAT is assigned PID=0, the PMT is assigned PID=1024, a video stream is assigned PID=501, an English version audio stream is assigned PID=601, and a Korean version audio stream is assigned PID=602.
A conventional IPTV service system adopts a multicast technology for an effective use of network bandwidth, a construction of which is illustrated in FIG. 2.
Referring to FIG. 2, the conventional IPTV service system includes: a broadcasting station 101 for producing broadcasting data in the form of MPEG-TS to transmit the same, a headend 102 for packetizing the MPEG-TS into IP packets for each broadcasting channel, multicast routers 103 and 104 for multicasting the packetized MPEG-TS for each broadcasting channel, and a set-top box 105 joining to a multicast group corresponding to a broadcasting channel selected by a user to receive the packetized MPEG-TS transmitted from the headend 102.
As illustrated in FIG. 3, the headend 102 performs packetization by segmentating the MPEG-TS into a predetermined size and then adding an IP packet header including a destination address and a source address. A multicast group address MGA corresponding to a channel is assigned as the destination address, and the address of the headend 102 that has performed the packetization is assigned as the source address SA.
Since various kinds of elementary streams are mixed in a packet output through the headend 102, it has been impossible for the set-top box 105 to selectively receive elementary streams of only a specific kind from the headend 102.
Consequently, the set-top box 105 receives elementary streams of even unnecessary.
In the conventional IPTV service system, because a set-top box 105 receives elementary streams of even unnecessary kinds, the network bandwidth usage is not efficient.
For example, when a user selects Korean on a broadcasting channel supporting a bilingual service of Korean and English, the set-top box 105 needs to decode and reproduce only Korean audio streams, but does not need to receive English audio streams.
However, according to the conventional art, since an element for blocking transmission of English audio streams is not provided, the sep-top box 105 constantly receives even unnecessary foreign language audio streams, wasting a bandwidth corresponding to the foreign language audio streams.
Also, the IPTV service supports a mosaic electronic program guide (EPG) service of simultaneously displaying a plurality of channels on one screen so that a user can select a desired channel more swiftly.
In the mosaic EPG, every TV channels to be appear on EPG screen are encoded as independent streams and then multiplexed into single MPEG-TS. This type of MPEG-TS, having multiple independent streams in it, is known as the multiple program transport stream (MPTS).
However, when the mosaic EPG is personalized, the TV channels to be included in the MPEG-TS varies with each user.
Since MPEG-TS should be constructed and transmitted for each individual, the MPEG-TS can not be multicast. Consequently, the efficient use of the network bandwidth can not be achieved.